Fixability and anti-offset property of toner used for electrophotography or the like are in a trade-off relation. How to harmonize the both is therefore an important issue in designing a binder resin for toner. The toner is also required at the same time to have a good storability, in other words, to be not causative of blocking, which is aggregation of toner particles, in a fixing unit.
Aiming at responding these requirements, there has been known a technique of improving the fixability at low temperatures, by introducing a crystalline component into the binder resin composed of an amorphous resin. Because the crystalline resin sharply melts and lowers the viscosity at around the melting point thereof, the resin can be lowered in the viscosity only with a small amount of heat energy, and therefore improvement in the fixability is expectable.
Publicly-known techniques for introducing a crystalline resin into the binder resin composed of an amorphous resin include:
(A) a method of hybridizing an amorphous resin and a crystalline resin on the molecular chain basis, in a form of block copolymer or graft copolymer (see Patent Document 1, for example);
(B) a method of blending a well-compatible combination of an amorphous resin and a crystalline resin, by a physical method of kneading such as fusion blending and powder blending (see Patent Document 2, for example); and
(C) methods of blending a less-compatible combination of an amorphous resin and a crystalline resin, by physical methods of kneading such as fusion blending and powder blending (see Patent Document 3 and Patent Document 4, for example).
However, the methods of (A) and (B) have failed in keeping a sufficient level of storability, because the amorphous portion and the crystalline portion are highly compatible, and a lot of crystalline polymer consequently remained ungrown to crystal in the amorphous portion. Therefore, a step of promoting and controlling the crystal growth, by annealing for a predetermined length of time, might be necessary (see Patent Document 5).
The method of (C) has raised difficulty in ensuring stability of toner characteristics, because the amorphous portion and the crystalline portion are less compatible, and diameter of dispersion of the crystalline resin was large as a consequence. Another known method is such as appropriately adjusting monomer composition of crystalline polyester and amorphous polyester, so as to control the compatibility between the both, and to thereby allow the crystalline polyester to disperse while keeping a diameter of dispersion of 0.1 to 2 μm (see Patent Document 6, for example). However, a problem in stability of toner characteristics remains unsolved even in this case, because the crystal size and the distribution thereof may vary depending on cooling conditions during manufacture of the binder resin and manufacture of the toner. Moreover, species of applicable monomers and composition are limitative.
Patent Document 7 describes a technique of manufacturing the binder resin, by polymerizing vinyl monomers under the presence of crystalline polyester having an unsaturated double bond on the molecular terminal.
[Patent Document 1] Japanese Laid-Open Patent Publication No. H4-26858
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2001-222138
[Patent Document 3] Japanese Laid-Open Patent Publication No. S62-62369
[Patent Document 4] Japanese Laid-Open Patent Publication No. 2003-302791
[Patent Document 5] Japanese Laid-Open Patent Publication No. H1-35456
[Patent Document 6] Japanese Laid-Open Patent Publication No. 2002-287426
[Patent Document 7] Japanese Laid-Open Patent Publication No. H3-6572